Control apparatus



March 18,1952

Filed Aug 15, 1945 A. E; BAAK CONTROL APPARATUS 2 SHEETS-$HEET 1 March 18, 1952 BAAK CONTROL APPARATUS 2 SHEETS-SHEET 2 Filed Aug. 13, 1945 Patented Mar. 18, 1 952 UNITED STATES PATENT OFFICE CONTROL APPARATUS Albert E. Beak, LosAngeles, Calif., assigncr to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn, a corporation of Delaware Application August 13, 1945, Serial No. 610,583

12 Claims. I

The present invention relates to apparatus for controlling the air pressure within an aircraft cabin.

The cabins of aircraft which operate at high elevations are commonly pressurized to prevent discomfort and other undesirable physiological difficulties among the users of the aircraft. Generally, the cabins are pressurized by supplying adequate quantities of compressed air to the cabin and controlling the air outlet from the cabin by suitable valve means. Various systems of control for the outlet valve are used but none of the prior apparatus has proven entirely satisfactory.

In considering the effect of varying air pressures on humans, it is noted that the average person has a rather wide tolerance to the pressures imposed on him, but this tolerance depends not only on the value of the pressure involved, but also its rate of change. Because of this, it is not only necessary to control the absolute pressure within the cabin, but also the rate of change of the pressure in said cabin. To the casual observer, it would appear that these diinculties could be entirely overcome by merely maintaining the atmospheric pressure of the airport in the cabin at all times, so that there would be no change of pressure and, of course, no rate, of change of pressure. In an aircraft, however, the necessity of weight reduction, the desire to fly at higher and higher elevations, and the difference in elevation of various airports at which the airplane may stop all combine to require changes in air pressure within the aircraft cabin.

The present invention meets the needs of a desirable cabin pressure control apparatus by permitting' changes in pressure. in the cabin proportionately to the changes in elevation of the aircraft up to the maximum pressure differential that can safely be withstood by the aircraft structure or to a limiting pressure for the human occupants.

It is thus an object of the present invention to provide apparatus for Varying or maintaining the pressure in an aircraft cabin in proportion to the altitude of the airplane.

It is a further object to limit the change in absolute pressure within an aircraft cabin to a predetermined value.

It is a further object to limit the differential It is'a further object to provide cabin pressure control apparatus wherein relatively few and simple specially constructed components are used.

It is a further object to provide cabin pressure control apparatus wherein the permissible rate of change of pressure may not exceed a value .proportionate to the rate of change of. elevation of the aircraft.

It is also an object to provide cabin pressure control apparatus wherein the low limitof 'pressure, in terms of altitude, may be readily adjusted and may be adjusted at a timedrate.

It is a further object to provide means for controlling cabin pressure wherein the controlling functions may be correlated byeither mechanical or electrical means.

These and other objects will become apparent upon a study of the following specification and drawings in which Figure 1 shows schematically the present/cabin pressure control apparatus. wherein the control components are electrically correlated;

Figure 2 is'a view'similar. to Figural, but wherein the control components aremechanically correlated.

Figure 3 is a sectional view'of the chaser switch taken on line 3-3 of Figure 2.

Figure 4 is an elevational view of modified limit adjusting means usable in the apparatus of Fig;- ure 2.

In the description of the present invention; it will be assumed that the aircraft-cabin in' question is adequately supplied with air; by means such as a compressor ll, under a pressure at least' as high as that desired in the cabin. The control of the pressure in the cabin is then effected by controlling the air outlet from the'cabirr;

While means may be employed to regulate the inflow of the air, such means forms no part'of the present invention and therefore has not-been, shown.

In Figure 1, valve [0 controls airflow through outlet I l mountedin wall l2 of the airplane. While valve i0 is shown as a single butterfly type, it may be of any suitable form capable of power actuation. Closing valve cluding armature 20 and field windings 2| and 22. This type of motor requires for-operation a difference in phase of the current supplied its windings, and the direction of rotation of the ar-- I 0 increases." cabin pressure, or increases the diiferential'of mature, such as 20, depends upon whether the current supplied winding 2I lags or leads the current supplied winding 22. Winding 22 of motor I is energized by the circuit: secondary winding 24 of transformer 25, wire 28, capacitor 21, wire 28, winding 22 and wire 29, back to secondary winding 24. As no means are provided for varying the phase of the current supplied winding 22, this winding is known as the fixed phase winding. Winding 2| is energized by the output of amplifier 39, the circuit being: terminal 3!, Wire 32, winding 2|, wire 33, and terminal 3 -3.

As above noted, the phase of the current supplied winding 2I, and thus the phase of the output current of amplifier 30, determines whether or not the motor will operate and the direction of rotation.

Amplifier 30 is of any suitable sort which will maintain the same phase relation in its output current as exists in the input current. As an example of a highly successful amplifier of this sort, reference is made to that disclosed in the copending application of Albert P. Upton, Serial No. 437,561, filed April 3, 1942, now Patent Number 2,423,534, issued July 8, 1947. Amplifier 38 includes signal input terminals 35 and 31 and the operating current for the amplifier is furnished by the circuit: secondary winding 38 of transformer 25, wire 39, terminal 49, terminal 5!, wire 42, and secondary winding 38.

Primary winding 44 of transformer is energized by the circuit: line wire 45, wire 46, winding 44, wire M, and line wire 48.

The phase of the signal current impressed on terminals 33 and 31 of amplifier 3%! depends on the condition of balance of a compound electrical network including individual networks 5% and5I. Network 59 receives its energizing current from secondary winding 55 of transformer 56 and includes resistors 51 and 58. Resistor 5'? is connected to terminal 59 of winding 55 by wire 60 and to intermediate tap EI by wire 62. Resistor 58 is connected to tap SI of winding 55 by wire 63 andto terminal 64 by Wire 65. Potentiometer Wiper I6 coacts with resistor 53 and is connected to terminal 31 ofamplifier by wire 66.

Potentiometer wiper 'II) coacts with resistor 5? and is connected to Wiper ll of network 5% by wire I2.

Primary winding I5 of transformer 56 is connectedto line wires and 48 by wires 76 and 11, respectively.

Network 5| is supplied current by secondary winding 80 of transformer 13! and includes resistors 82 and 83. Resistor 82 is connected to terminals 84 and 85 of winding 86 by wires 86 and 81, respectively, while resistor 83 is connected to said terminals 8t and 85 by wires 88 and 89, respectively. The aforementioned potentiometer wiper II coacts with resistor 83 while potentiometer wipe 9i) coacts in a similar fashion with resistor 82. Wiper 9c is connected to terminal 36 of amplifier 30 by wire 9I thus completing the compound network.

Primary winding 92 of transformer 8I is connected to line wires and it by wires 93 and 9%, respectively, it being noted that the transformers are similarly connected so that networks and 5| will be energized by currents of like phase.

Wiper III is adjusted over resistor 57 by a differential pressure responsive device IIlI whenever the cabin pressure exceeds the atmospheric pressure by a predetermined value. This device safeguards the aircraft structure by limiting, in a manner to be shown, the amount of differential pressure that can be imposed on said structure. Device Illl comprises a spring expanded bellows I02, the interior of which is connected to the atmosphere by tube I03 extending through cabin wall portion H2. The expansion of bellows I02 is limited by stop means Hi4 and the motion of bellows N32 is communicated to wiper I0 by link means I95.

Ratio controller III operates wiper ll over resistor 83 to serve as the effective regulating device for the cabin pressure. Controller III comprises a spring expanded evacuated bellows II3 for responding to the absolute pressure in the cabin, bellows I I3 being connected to pivoted lever H4 and to link H5 by link IIii. At the other end of lever lid, link II? connects said lever II i to bellows IIB. Bellows H8 is connected to the atmosphere by tube H9 extending through wall portion I253 of the aircraft cabin. Bellows IIB thus responds to the difference between cabin pressure and atmospheric pressure. Lever H4 is carried by a longitudinally shiftable block means I2I pivotally mounted on a threaded member I22. Member I22 is longitudinally adjusted by screw means I23, having an adjusting knob I26, and is guided by means I25. By manipulating knob I24, means I22 and member I2I is adjusted along lever I l t, thus shifting its pivot point and varying the relative effectiveness of bellows H3 and H8 for adjusting wiper H. For the purpose of this description, it will be assumed that the pivot point for lever IIQ is midway between the ends so that bellows H8 and H3 are equally effective in adjusting wiper 'I I.

Since bellows I i3 responds to the absolute pressure in the cabin, it, acting alone would adjust wiper ii in a manner to hold the cabin pressure constant by moving said wiper to the left with any decrease in the cabin pressure. Bellows II8, as before noted, responds to the different atmospheric and cabin pressures and, acting alone, would adjust wiper 'II in a manner to make the cabin pressure correspond to the atmospheric pressure. Thus, a decrease in atmospheric pressure would cause movement of wiper 'II to the right to decrease cabin pressure. The manner in which wiper lI adjusts the cabin pressure will become apparent in the description of operation of the present apparatus which shortly follows.

Because the aircraft may use airports of different elevations, it is necessary that the low limit, in terms of altitude, or the reference pressure, must be adjustable. To perform this function, device IE3 is provided for adjusting wiper 9t. Device I38 comprises an evacuated bellows I3I which is expanded by an adjustable tension spring I32 acting through member I33, said member being secured at one end to said bellows and attached at the other end to one end of said spring I32. Member I33 is also pivotally secured to wiper 99 so that any movement of said member causes movement of said wiper over resistor 82. The other end of spring I32 is attached to a threaded member itd which may be longitudinally adjusted by threaded shaft I35. Threaded shaft IE5 is driven through reduction gearing I36 by reversible motor means I31, and member I3 2 is prevented from rotating with said shaft by guide means I38.

The energization of motor I3? is controlled by a chaser switch construction including a contact member Mt carried by member I3 3 which coacts with flexible and resilient switch blades MI and H32. Blades MI and I 32 are insulated from each other by and mounted on block I43 which in mini mou te O shaf l fl- B a e 1. 1 an 15 su i en pa e an re 5. rra d that they straddle and may each be slightly spaced from contactmember [4p and the blades are each sufliciently flexible that block I43 may be considerably rotated even though contact member Iliii has not moved. Obviously, anyrotaticnof block I43 brings one or the other of the blades in contact with member I45. As before noted, block I43 is mounted on shaft I44. Shaft I44 is rotatably adiustedby knob"I45"and th'e shaft is maintained in adjusted positions by sui'table friction bearing means such as I46, it being necessary that the frictional force of the hearings or the like exceeds the rotativeforce on the's'haft that may arise" fromthe deflection of one of "the switch blades of the'chaser switchi Knob I45 includes pointer I41 for use with a suitably graduate'dscal'e I48l' M The energizing circuits for motor I3! include a speed controlling'rheostat I55 having a wiper I5 I' and resistor I52. Whena circuit iscompleted througli'the blade MI, "sh'aft' I35'is' driven in a"di'rection to cause'membe'r'lii l'to move to the right, andtighten spring" I32, whereas the circuit made through blade H2 causes's'haft' I35 to be driv'ninadirection to move I34 to the left and loosen springlaz. Rhostat I51! controls the speed of'the 'motor' andthus the rate of change of the springftension. "Because spring I32, bellows I3'I,"r'ne'mber'I33,' and wiper iiilar aliconnected, tli"po's'ition"ofwiper 90 is dependent on the position of bellows I3I which in turndepends on thecabin pressure and the tension of spring I32. Bellows I3I' is expanded to'itsmaxirn'um under atmospheric pressure conditions only by maximum tension on'said spring. Either "an increase in pressure on the bellows or decrease in tension of the spring will cause wiper 90 to move to the left whereas an increase in spring tension or a decrease in cabin pressure will tend to move said wiper-tothe right. The operation of device I30 and its part in the control of cabin pressure will be made more clear in the following description of operation.

While the various components and their relation has been rather specifically set forth in the preceding description, it is noted that many substitutions and equivalents are apparent and are contemplated in the invention.

Operation of Figure. 1

In considering the operation of the present apparatus, the present description can be made more concrete by making certain assumptions. First a good starting place for the description will be that in which the airplane is at rest on an airfield at sea level elevation. At sea level, and with no cabin pressurizing needed, it is obvious that the differential pressure is zero, hence bellows I02 of differential pressure responsive means IIII is expanded against its stops. This device may be considered as being of such strength and so adjusted that it will move wiper III, to the left across resistor 51 only when the differential pressure imposed on bellows I02 exceeds about Hg. With a differential pressure of less than 10" of Hg, imposed on bellows I02, wiper Illremains at its extreme right position.

With zero elevation of the aircraft and maximum absolute pressure imposed on bellows H3, and with no differential pressure imposed on bel- 10Ws II8, wiper II is adjusted to the extreme rightofresistor 83. Any increase in altitude, or

decrease in; absolute pressure, on. bellows. l. 3..W i1 .l

6 us hesam expand n t m r Wip r to the left, s previously explained. However, the motion will be modified by the increase in differential pressure occasioned as the aircraft rises and pressure in the cabin increased relative to atmospheric changes in pressure. It has previouslybeen noted that'knob I24 is soadjusted thatbellows II8 will be equally cffectivein'con trolling the motion of wiper II as will the bellows I I3, hence apparatus III will control wiper II in a manner to hold the cabin pressure at a value substantiallymid way between atmospheric pressure at sea level and atmospheric pressure atth a qnin e ti Rheostat I50 is so adjusted that motor I3] cannot operate wiper across resistor 82 at a rate to vary cabin pressure at more than 300 feet per minute. With sea level pressure, and spring I32 at maximum tension due to knob I45 being adjusted to zero, wiper 90 is at the extreme right of resistor 82. Should knob I45 be rotated clockwise, and spring I32 thereby loosened, wiper 90 would then move to the left across resistor 82 due to the cabin pressure collapsing bellows I3 I'.

To more readily understand the compound network, it may be assumed that secondary 30 of transformer 81 imposes 30 volts across resistors 32 and 83. Likewise, 3O volts are impressed across resistor 57 and 15 voltsacross resistor 58. In addition, it may be considered that the polarity of networks 50 and EH is such that the left of each of said networks is negative and the right-hand of said networks is positive in polarity.

While it is obvious that the networks are energized by alternating current, it is noted that a current whichis at one instant negative in potential is, electrical degrees later, positiv in potential. It is apparent that a shift in phase may be interpreted at a specified instant as a variation in the polarity of the voltage. Con sidering the phase relation of the compound network in terms of potential, it follows that a difference in potential across terminals 36 and 3'l of amplifier 30 will cause operation of motor I5; if terminal 36 be positive relative to termin al S'I during an assumed half cycle, Inotor I5 operates in a direction to close valve Ifl whereas, if terminal 31 be positive relative to terminal 38 during the same half cycle, motor I5 operates valve III in an opening direction. Opening valve In will tend to decrease cabin pressure, relative to atmospheric pressure, and closing said valve will tend to increase cabin pressure, relative to atmospheric pressure,

Starting with wiper I5, and considering the balance of the network in the apparatus as shown, it is noted that wiper I6 is connected through to wiper I0 by wires 63 and 62, hence they are at the same potential. Further, wiper I0 is connected through wire 12 to wiper. II which in turn is connected through wiperv 90 by wires 89 and 81. Therefore, wipers I6 and 90 are at a like potential; hence, terminals 31 and 36, connected to said wipers, respectively, are at like potential, there is no signalimpressed on amplifier 30 and motor I5 does not operate.

If the airplane should now leave the field and climb at a rate of, for instance, 600 F. P. M., the air pressure in the cabin will tend to decrease at the same rate as the outside atmospheric pressure due to valve In being open. However, as thecabin pressure tends to decrease, bellows II3 expands and moves wiper II to the' left. With each of the other wipers in their previous loca;

7 tions and with wiper II moved 2 bolts, for instance to the left across resistor 83, wiper 90 then becomes 2 volts positive relative to wiper I6 during the half-cycle being considered, terminal 36 becomes 2 volts positive relative to terminal 31 and motor I operates to close valve I0. The closing movement of valve I0 also moves follow-up potentiometer wiper IE to the right across resistor 58, this movement continuing until wiper I6 has moved 2 volts to the right across said resistor. Then, wipers l0 and II will be 2 volts negative relative to wiper It and wiper 80 remains 2 volts positive relative to wiper H. The sum of the unbalance equals zero and again there is no potential across terminals 36 and 3i of the amplifier. The motor is stopped. As the valve is moved toward closed position, pressure increases in the cabin in a manner to restore the previous value and to cause retraction of bellows I I3. In addition, however, increase in cabin pressure likewise causes an increase in differential pressure between the cabin and the outside, hence bellows II8 tends to contract and to modify the action of bellows H3 in moving wiper Ii. Actually then, as valve I0 starts to influence the cabin pressure, wiper H is moved by the joint action of bellows H3 and I I8, so that valve i0 is controlled by the joint effect of cabin pressure and differential pressure. This will be seen by noting that there is no extension of bellows H3, and no force exerted by the same when cabin pressure of an aircraft at a high altitude is at a sea level value whereas, at this same value of cabin pressure, the force due to bellows H3 is at a maximum. If the cabin pressure should be changed to correspond to the altitude of the aircraft, then bellows H3 would be forced by its internal spring to expand a predetermined amount and no force would be exerted by bellows H8. However, expansion of bellows H3, and the consequent movement of wiper I i, would tend to restore sea level cabin pressure. Therefore, due to the connection of the two bellows by lever H4, and the joint effect of bellows H3 and H8, wiper H is moved across resistor 83 only half as far as it would if bellows H3 alone were controlling. Therefore, when the aircraft reaches an elevation of 1,200 feet, for instance, the cabin pressure will be controlled to a value equivalent to 600 feet of elevation. So far, there has been no effect on the other control devices because the differential pressures involved are still far below those necessary to cause operation of device IOI and a decrease in absolute cabin pressure only tends to move wiper 90 to the right but it is already at its extreme right position. As the aircraft continues to rise, the differential pressure tends to increase; therefore valve I0 is continually moved to a more closed position even though the absolute pressure in the cabin is decreasing. Therefore, wiper 'II gradually shifts to the left across resistor 03 sufficiently to cause sumcient valve closing movement to maintain the desired condition of a cabin pressure one-half that, in the terms of altitude, of the elevation of the aircraft. If, at a particular elevation, it should require valve I0 to be half closed to maintain the desired cabin pressure, and the half-closed valve position meant that wiper I6 would be 7 /2 volts positive relative to wiper "I0, then wiper H would have to move A the distance across resistor 83 to the left so that wiper H might be 7 /2 volts negative relative to wiper 00 to balance out the network.

If it be assumed that an 8,000 foot cabin, or

pressure corresponding thereto, is a maximum for the passengers, and it is desired to fly the airplane at an elevation exceeding 16,000 feet, this can be done by adjusting knob I24. Instead of maintaining a cabin pressure which is in terms of altitude, of the elevation of the airplane, apparatus I II may be adjusted to maintain a cabin pressure of V or other fraction, of that of the elevation of the airplane by adjusting knob I26 to move the pivot block I2I along lever H4 and thus vary the effect of bellows H8. Thus, bellows H3 is made more effective in maintaining the absolute pressure of the cabin, with the above noted adjustment. However, because the absolute pressure at an 8,000 foot elevation is approximately 22.2 inches of Hg, and differential pressure responsive device IOI moves wiper I0 to the left upon a differential pressure in excess of 10 inches of Hg, then the desired maximum differential of pressure tends to be exceeded as the aircraft rises above 23,000 feet, corresponding to a 12.2 in. of Hg, pressure. This causes movement of slider I0 to the left. Movement of wiper I0 to the left makes it negative relative to wiper I6 and decreases the positive signal to terminal 30. Because wiper I6 is then more positive relative to terminal 36, than it was previously, or, assuming that the apparatus was in a state of equilibrium when wiper it moves to the left, wiper I6 and terminal-31 then become positive relative to terminal 36 and motor I5 is operated to open the valve I0. Opening valve I0 decreases the cabin pressure and therefore decreases the difierential pressure, hence device IOI is effective in limiting the differential pressure that can be imposed on the aircraft structure.

If the aircraft should now descend to the field from which it took ofi, no adjustment of the apparatus is necessary, the absolute cabin pressure tends to increase due to the lessened differential across valve I0, and bellows H3 is thus forced to contract and move wiper H to the right to open valve I0.

If the aircraft is to land at a field having an elevation different from that where it took off,

knob I65 is adjusted so that pointer Id! indicates the elevation of the new field. If this field be at an elevation of 4,000 feet, for instance, knob I45 is rotated so that pointer I i? is vertical and block I03 is rotated in a similar fashion. Blade I4! will also be vertical but blade I02 will be in contact with member I00 and considerably deflected. However, when blade I 32 comes in contact with member I 30, a circuit is closed through motor I31, as follows: battery I53, resistor I52, wiper I51, wire I55, contact member I40, blade I42, wire IE3, motor I37, and wire I5? back to battery I53. This causes motor I3! to drive member I34 to the left, which motion will continue until blade I42 is no longer deflected and member I40 moves out of contact with it and breaks the circuit. The motor is thus deenergized and stopped. However, movement of I34 to the left loosens spring I32 and permits wiper to be shifted to the left. As wiper 90 moves to the left, it becomes more negative than it previously was, or otherwise stated, wiper I6 and terminal 31 of amplifier 30 become more positive relative to terminal 36. As before noted, when terminal 31 becomes positive relative to terminal 36, motor I5 is operated in a valve opening direction. Opening of valve l0 permits the absolute cabin pressure to decrease. While. a decrease in pres-.=

sure in the cabin is reflected in a movement of wiper II to the left due to the expansion of bellows I I3, it is noted that wiper II must move to the left of wiper 90 before terminal 36 will normally become positive relative to terminal 31 and again cause a closing movement of the valve. Wiper 90 thus forms a reference point determining the high limit of absolute pressure, or the low limit of pressure in terms of altitude pressure at which device III will control. Because movement of wiper 90 to the left is immediately reflected in a reduction of absolute cabin pressure, it is important that the movement of wiper 90 should not exceed a desired rate. As before pointed out, the speed of motor I3! is controlled by rheostat I50 so that the spring tension of I32 can be varied at a desired rate. In addition, it is noted that even if spring I32be sufficiently loosened so that wiper 90 will be at the mid-point of resistor 82 at a cabin pressure corresponding to a 4,000 foot elevation, at an elevation in excess of 4,000 feet, wiper will lie to the right of the mid-point because the positioning of wiper 90 is due to the joint effect of spring I32 and bellows I BI. Wiper 90 will move to its mid-position as the absolute cabin pressure increases and causes contraction of bellows I3I.

Without the adjustment of wiper 00 to compensate for the new elevation of the air field at which the landing is to take place, it is noted that the cabin pressure would tend to correspond to that of a 2,000 foot elevation when the plane is landing at 4,000 feet. While this excess of pressure, absolute, would be quickly dissipated when the compressor for the cabin was shut oif due to the air flowing back through the same, the change in pressure would be at too rapid a rate, and therefore undesirable. Under other flight conditions, such as when the aircraft leaves a field at zero elevation for instance, and rises to an elevation of about 8,000 feet, and maintains this elevation for the duration of the flight and then lands at a field having an elevation of 5,000 feet, it is noted that complications tend to arise. While the aircraft is rising to an elevation of 8,000 feet. the cabin pressure is changing to a value corresponding to 4,000 feet, and then when the aircraft goes down to the 5,000 foot elevation field, the cabin pressure tends to go to a value corresponding to 2,500 feet elevation. Here again, on landing, the excess pressure could be relieved by blowing back through the compressor when the compressor or like is stopped. However, by, adiusting device I30 prior to the descent to the landing field, valve I0 will be driven toward open position and the pressure in the cabin. in terms of altitude, increased so that t e cabin pressure will correspond to that of the field when the landing actually takes place. Because of the til-ed rate of adjustment of wiper 90, it is noted that knob I45 must be adjusted to the elevation of the field sufliciently long before the landing is to be attempted so that there will be time to properly adjust wiper 80. In other words, if wiper 00 is to be adjusted at a rate to change cabin pressure at 300 F. P. M. and knob I is adjusted from zero to 5,000 feet. then knob I05 must be adjusted approximately 1'? minutes before the landing is to be effected.

When knob N55 is again turned to zero and blade MI is brought into engagement with M0, motor I3! is energized to move I30 to the right by the following circuit: battery I53, wire I5 1, resistor I 52, wiper I5i, Wire I55. contact member' I43, blade I4I, wire I56, motor I37, and wire 10 I51 to battery I53. Member I34 will move to the right until contact member I40 moves out of engagemnet with blade I 4I, as shown.

The present apparatus is thus seen to be fully effective in varying aircraft cabin pressure at a proportionate rate to change in elevation of the aircraft. In addition, overstressing of the aircraft structure is prevented by simple differential pressure responsive means. Further, the cabin pressure can be adjuted from any particular value to a desired value at a timed rate. On many of the flights that an aircraft makes, no adjustment whatever would be required on this control apparatus, and on other flights, where landing is to be made at a different elevation from the field of the take-off, only a single knob need be adjusted. In addition, if flights at excessive elevations are made, an adjustment of knob I24 might be necessary.

Figure 2 Figure 2 shows apparatus which will function somewhat similarly to that of Figure 1, but wherein the various components are mechanically correlated instead of electrically as in Figure 1 In Figure 2, valve member 20! controls airflow through air outlet 202 extending through cabin wall 20%. Valve 20I is adjusted by shaft 204 driven through reduction gearing 2&5 by motor means 205. Motor means 206 is of a two-phase type similar to that described in Figure 1 and comprises an armature 20?, a field winding 208, and another field winding 200. Winding 209 is energized from secondary 2 II) of transformer 200 by the circuit: secondary winding 2I0, wire2I I, condenser 2I2, wire 2I3, winding 209, and wire 214 back to secondary winding 2I0. Winding 208 is energi ed from the output 'of amplifier 2I5 by the circuit: output terminal 2I6, wire 2 I1, winding 203, wire 2 I3, and terminal 2 I 9.

Amplifier 2 I5 is of a type which maintains the phase relation of its output current the same as the phase relation of the signal current impressed on its input terminals. Thus this amplifier is similar to 30 in Figure 1. Amplifier 2I5 receives an ener laing current from transformer secondary winding 220 by the circuit: winding 225, wire 22I, terminal 222, terminal 223, wire 22 i, and secondary winding 2I2. Primary winding 225 of transformer 200 is energized from line wires 22% and 22'! by wires 228 and 229, respectively.

In addition to valve as: being operated by shaft 205, potentiometer wiper 230 is driven by said shaft across resistor ZSI of network 232. Network 232 also includes res stor 233, and is energized by secondary winding 234 of transformer 235. Resistor 234 is connected to output terminals 236 and 23'! of winding 234 by wires 233 and 239, respectively. Resistor 233 is connected to terminals 233 and 23's by wires and EM, res ectively. Primary winding of transformer 235 is energized by the circuit: line wire 226, wire 243, primary winding 2 .2, wire 244, and line'wire 221. Wiper 230, which sweeps over resistor 23I is 'con nected by wire 255 to signal input terminal 246 of amplifier 2I5. Wiper portion 248 of lever mem- 200 is adjustable over resistor 23% and is coned by wire 253 to input terminal 25I of said ler. Wiper portion 243 is electrically insulated from lever portion 200 by insulation 252.

Lever is p-ivotaliy mounted on support 254 and is connected by strain release means to lever also pivotally mounted on said support memits her. Lever member 240 includes an angularly extending abutment member 255 for engaging lever 255 for limiting the counter-clockwise rotation of lever 248 relative to lever 255. Projecting member 256 is held in engagement with lever 255 by tension spring means 25'! extending between levers 249 and 255. Levers 228 and 255 thus tend to rotate together although lever member 248 can rotate clockwise relative to 255 if the force of spring 251 is overcome. The right end of lever 255 is connected by link means 268 to absolute pressure responsive bellows 26!. Bellows 26! is evacuated and is prevented from collapsing by a spring 262. An expansion of bellows 26! rotates levers 255 and 249 counterclockwise and moves wiper portion 248 to the right across resistor 233.

Counterclockwise rotation of lever 255 is opposed by means including pivoted lever means 265. Lever means 255 is pivoted at its right end to support means 266 and carries a transversely projecting pin 261 at its left end. Lever 255 coacts with lever 255 through a relatively lon spring blade 218 having a socket portion 21! for engagement with thrust member 212. Thrust member 212 engages a socket portion 213 in the left end of lever 255. Spring blade 218 is long enough to overhang the right end of lever 285 so that movement downward of the left end of lever 265 results in a tendency for socket portion 21! of lever 218 to move upwardly. Deflection of spring 218. relative to lever member 265 is permitted by off-setting one portion of lever 265 relative to the other, as at 214, or by mounting said spring 218 on a block member carried by lever 265, not shown. At an intermediate point 215 of said lever 265, differential pressure responsive bellows 216 is pivotally attached.

Bellows 216 is exposed to cabin pressure on one side, and the inside of said bellows connects through tube 211 to receptacle 218, which in turn communicates with the outside temperature through adjustable restrictor means 219 and tube 288. Bellows 216 is in a normally expanded position due to its own spring rate but if desired, a suitable spring may be placed inside the bellows to keep it in a desired expanded position at minimum differential. However, as the differential of pressure increases, such as when the aircraft rises into the air and pressure is built up in the cabin, bellows 216 tends to contract and rotate lever 255 counterclockwise. Due to the aforementioned overhang of spring 218, socket 21! tends to move upwardly and thereby imposes a force on lever 255 tending to rotate it clockwise, or against anyexpansive forces of bellows 25!. Or, in terms of movement of wiper 258, contraction of bellows 216 tends to move said wiper 248 to the left across resistor 233. Bellows 218 and 26! are preferably proportioned so that they are about equally effective in causing motion of lever 289.

In addition to bellows 26! and 216 determining the movement of levers 228 and 255, differential pressure responsive bellows 28! may also influence the position of lever 249. Bellows 28! operatesa link member 282 which has a transversely extending abutment 283 adapted to engage lever 249 under circumstances to be related. The motion of member 282 is limited by a. fixed pin 284 coacting with slot 285 in said member 282. Lever member 282 is normally in its extreme right position due to the force of adjustable spring means 285. Bellows 28! is connected by tube 281 to tube 288, and therefore communicates with the outside atmosphere. As the outer side of bellows 28! is exposed to cabin presusre, bellows 28! responds to the differential between cabin pressure and atmospheric pressure. When this differential reaches a limiting value, such as 10 in. Hg, bellows 28! contracts and moves member 282 to the left against the force of spring 286. When the movement to the left of member 282 is sufficient that abutment portion 283 engages lever 2&9, lever 249 is also moved to the left to cause an opening movement of the outlet valve. Lever 249 is permitted to move to the left even though lever 255 does not movedue to the force of bellows 28! overcoming strain release spring 251.

Adjustable stop means are provided for coaction with transversely extending pin 26! of lever 265 to provide upper and lower limits of cabin pressure, in terms of altitude. For the upper limit, cam 298 is driven through shaft 25! by adjustment means 292 to provide a variable stop limiting the downward movement, or the counterclockwise movement of lever 265. Limiting the counterclockwise movement of lever 265 thus limits the force that can be exerted by lever 218 on lever 255 so that, upon pin 261 engaging cam 298, control of the apparatus tends to shift to absolute pressure responsive bellows 25!. In the position shown, cam 298 is rotated by 292 to a maximum pressure limit, in terms of altitude. Rotation of 292 to the left or counterclockwise limits the deflection of lever 265 to a lesser amount and imposes a lower limit on cabin pressure, in terms of altitude. Adjusting means 292 is shown as a screwdriver adjustment device, but if desired this may be an ordinary thumb operated knob.

To provide a low elevation limit of pressure, cam 283 is mounted on and operated b'y shaft 295. Shaft 294 also drives switch drum 295 which is part of a chaser switch assembly. shaft 294- is driven through reduction gearing 295 by motor 281, said motor being of the reversible type such as I51 described in Figure 1. The chaser switch assembly is completed by an insulating block 298 mounted on shaft 289, said shaft 298 bein adjusted by knob 388. Block 299 carries a sprin switch blade 38! which engages drum 295 in a manner better shown in Figure 3. w

Figure 3 is a section taken on the line 8-8 of? Figure 2 and shows the construction of drum 295 and its coaction with blade 38!. Drum 295 comprises a core portion of insulatng material 382, and contact sector plates 383 and 385. Each of plates 383 and 384 extend a little less than half the way around said drum, so that the ends of said plates are spaced from each other by dead spots 385 and 385. In the position shown, blade 38! is on dead spot S85, hence it is not contactingeither blade 383 or 38 1. However, clockwise movement of blade 38! relative to said drum would bring said blade into contact with 383, whereas counterclockwise movement of said blade would bring it into Contact with made 305.

Motor 291 is controlled by the present chaser switch arrangement in the same manner and for the same reason as expressed in Figure l. Clockwise rotation of knob 388 energizes motor 291 in a manner to drive cam 283 clockwise. Although knob 588 and cam 293 are in their extreme counterclockwise positions, corresponding to a minimum low elevation adjustment, it is noted that a counterclockwise adjustment of knob 388 would cause a counterclockwise adjustment of cam 283 from a higher setting. The speed of motor 291 is governed by the setting of rheostat wiper 814 which in turn is adjusted by means 328. Adjustment means 328 is shown as a screw erted by 210 limited, any further increase in aircraft elevation, and any tendency of the aircraft cabin pressure to rise still higher, in terms of altitude, is resisted by the growing preponderance of control effort exercised by absolute pressure responsive bellows 26 l. Thus, by limiting the deflection of arm 265, and the force that can be exerted by spring 2T0, an upper limit of cabin pressure is established.

Should, for any reason, the differential between cabin pressure and atmospheric pressure exceed a desired limit, bellows 28l contracts and moves abutment 283 to the left against the force of spring means 2536. Upon abutment 283 engaging arm 2:19 and moving the same to the left, valve is driven open and thereby permits cabin pressure to diminish and thus lower said differential pressure.

If the aircraft should now return to the field from which it took oi, the cabin pressure would be varied in reverse order to that just described. However, if the aircraft is to alight at a field having a different elevation from the one previously mentioned, knob 300 is adjusted to the altitude of the new field and, operating through the chaser switch, motor 291 drives cam 293 to a position limiting the upward travel of pin 287. This insures that spring 270 will exert at least a minimum force opposin bellows 26l suiiicient to prevent the cabin pressure from dropping below, in terms of elevation, the elevation of the field at which the landing is to be made. While the motor 29'! operates cam 293 at a timed rate, the timed rate is of little importance if the altitude of the aircraft at the time of making the adjustment is more than twice that of the field at which the landing is to be made. However, if the altitude of the new field is more than half the elevation that the plane is flying at when the adjustment is made, it becomes apparent that the cabin pressure, in terms of altitude, must be increased for it normally is at a value half that of the aircraft elevation. Upon adjusting knob 300 to a new value, such as 5,000 feet, blade 30! engages contact sector 303 and energizes motor 291 by the circuit; battery 3H1, wire 316, resistor 3l5, wiper 3M, wire M3, blade 30!, sector plate 393, wire 1H2, motor 291, and wire 3 back to battery 3 l B. This drives cam 283 in a clockwise direction at a timed rate until dead spot 305 engages blade 3!!! and contact is broken with sector plate 303. However, pin 26! may not be in engagement with the cam in the initial movement of the same.

Therefore, cam 293 will have no effect on pin 26? until it advances to a position corresponding to the pressure within the cabin. From then on, however, pin 26'! will be depressed and spring 210 will exert greater force at a rate depending on the speed of advancement of cam 293. As the pressure will be varied in response to this movement, the necessity for the timed rate becomes apparent. If knob 330 be rotated counterclockwise, blade Bill would contact plate 304 and motor 291 would be energized through wire 3H to drive cam 293 counterclockwise until a dead spot is reached as before.

The operation of the apparatus of Figure 2 will be precisely the same when the control means of Figured is used with the exception, of course, that the lower limit of cabin pressure, in terms of altitude, will be varied immediately with adjustment of arm 325. As pointed out above, however, this is perfectly feasible providing that the aircraft flies at an elevation at least twice the height of any field at which it will alight and that'the adjustment of arm 325 be made at a time when the aircraft is more than twice the elevation of the field at which it is to land. Thus, the simpler version of control shown in Figure 4 is entirely practical for many of the routes over which aircraft travels.

If it be desired to further control the rate of pressure change so that it will be less than the normal change occasioned by the ordinary operation of the apparatus, restrictor 219 may be adjusted to slow the rate of response of bellows 216 to outside atmospheric pressure. By use of capacity storage means 278 and resistor 219, the time of response of bellows 216 in changing the differential pressure can be varied at will and as the response is slowed, bellows 26I gains dominance and tends to control the pressure to a fixed value. With bellows 26! opposed by a slower movement or adjustment of spring 210, the rate of change of pressure is definitely slowed, with the previously described rate of half the airplane climb rate as an upper limit. In fact, by closing restrictor 279, the aircraft cabin pressure can be maintained at nearly uniform value by bellows 26I alone.

In the preceding descriptions, the aircraft cabin pressure has been referred to in terms of altitude, and it has been assumed that the pressure would vary in proportion to the altitude. This is not strictly true, of course, for the elevation tends to increase at a more rapid rate than the absolute pressure decreases. The present description in which cabin pressure has been referred to in terms of altitude could just as well be made entirely in terms of absolute pressure, but it appears that those who use the aircraft and work with them are accustomed to refer to cabin pressure in terms of altitude.

The present specific examples are given only to properly illustrate and describe the present invention, and are not to be considered as limiting the same to the present embodiments. It is therefore intended that the scope of the present invention be measured only by the appended claims.

I claim as my invention:

1. In a structure subject to varying atmospheric conditions, an enclosed compartment in said structure, means for supplying air to said compartment, air outlet means for said air, electrically controlled means for varying the air pressure within said compartment, means including first variable electrical impedance means for responding to absolute compartment pressure, means including second variable electrical impedance means for responding to the ratio of compartment pressure to atmospheric pressure. means including third variable electrical impedance means for responding to differential pressure in excess of a predetermined value, and electrical network means including said first, sec- 0nd, and third impedance means for controlling said electrically controlled means.

2. In a structure subject to varying air pressure and having a supply of air under pressure, outlet means for said air, electrically controlled means for varying the air pressure within said structure, means including first variable electrical impedance means for responding to the absolute pressure in said structure, means including second variable electrical impedance means for responding to the ratio of pressure in said structure to atmospheric pressure, and balanceable electrical network means including said 17 first and second impedance means for controlling said electrically controlled means,

3. In an enclosed compartment subject to varying atmospheric pressure and having a supply of air under pressure, outlet means for said air, electrically controlled means for varying the air pressure within said compartment, means responsive to the ratio of compartment pressure to atmospheric pressure, electrical pedance means varied in response to said ratio responsive means, and balanceable electrical network means including said impedance means for controlling said electrically controlled means.

4. In a structure subject to. varying atmospheric pressure and including an enclosed compartment in said structure furnished air under pressure, means for regulating air flow through said compartment, means for controlling said regulating means, means including an adjustable electrical impedance responsive to absolute compartment pressure, means including another adjustable electrical impedance responsive to the differential between compartment pressure and the atmospheric pressure, and means coupling said compartment pressure responsive means and said differential pressure responsive means for dependent cooperative action in adjusting said controlling means, said coupling means including a variable ratio linkage.

5. In a structure subject to varying atmospheric pressure and including an enclosed compartment supplied with air under pressure, air outlet means for said compartment, means for varying the air pressure within said compartment, adjustable means for regulating said varying means, means responsive to the absolute compartment pressure, means responsive to the differential between compartment pressure and the atmospheric pressure, adjustable flexible means coupling said compartment pressure responsive means and said differential pressure responsive means for cooperative action in adjusting said regulating means for said varying means, and time controlled means for adjusting said flexible means.

6. In control apparatus, pivoted lever means movable in response to a condition indicative of a need for operation of said apparatus, stop means for one end of said lever means, manually adjustable switch means, motor means for adjusting said stop means, and switch means adjusted by said motor means cooperating with said manually adjustable switch means for controlling said motor means.

7. In a habitable structure supplied with air under pressure and surrounded by atmospheric air under less pressure and having means for varying the air pressure within said structure, control means for said varying means comprising, in combination, one means responsive to the air pressure within said structure, other means responsive to the difference of the pressure within said structure and the amospheric pressure surrounding the structure, flexible means operatively connecting said one means and said other means, means for con-trollably delaying the response of said other means to changes in atmospheric pressure, adjustable stop means limiting the amount of response of said other means to differences in pressure, and means controlled by said one means and said other means for regulating said varying means.

8. In a structure supplied with air under pressure and surrounded by atmospheric air under less pressure and having means for varying the air pressure within said structure, control means for said varying means comprising, in combination, one means responsive to the air pressure within said structure, other means responsive to the difference of the pressure Within said structure and the atmospheric pressure surrounding the structure, lever means jointly controlled by said; one means and said other means for regulating said varying means, said lever means including a rigid portion and a resilient portion and additional means responsive to the diiTerence of the pressure within the structure and the outside atmospheric pressure connected in operative relatiOn to said jointly controlled means for limiting said; diijerence in pressure to a predetermined value.

9. In control apparatus, a movable member, pivot means, first adjustable stop means for said member, said stop means including a lever carried by said pivot means and having an indicat ing portion and an oppositely disposed cam shaped stop portion for coasting with said member to variably limit motion in one direction, and second adjustable stop means for said member comprising a lever mounted on said pivot means and having an indicating portion at one end and cam means at its other end for adjustably limiting movement of said movable member in the opposite direction.

10. Control apparatus for a pressurized compartment comprising, in combination, means for controlling air flow through said compartment, means including a voltage dividing electrical circuit responsive to compartment pressure, means connected to said circuit and responsive to the difierential between compartment pressure and atmospheric pressure, and circuit means for connecting said pressure responsive means and said difierential pressure responsive means in joint controlling relation to said flow controlling means.

11. Cabin pressure control apparatus for an aircraft comprising, in combination, air flow controlling means, means responsive to the ratio of cabin pressure to the atmospheric pressure, means for connecting said ratio responsive means in controlling relation to said flow controlling means for regulating said flow controlling means in a manner to hold said ratio constant during normal flight conditions, means responsive to the absolute cabin pressure, means connecting said absolute pressure responsive means to said ratio responsive means in a manner to provide a high limit for absolute pressure in the cabin, and motor operated means for adjusting said absolute pressure responsive means at a predetermined ra e.

12. Pressure control apparatus for an aircraft cabin having a pressure varying means comprising, in combination, means responsive to the ratio of cabin pressure to atmospheric pressure, means for connecting said responsive means in controlling relation to said varying means, stop means for providing an adjustable high absolute pressure limit for said control apparatus, and time controlled means for establishing an adjustable low absolute pressure limit for said control apparatus.

ALBERT E. BAAK.

(References en following page) 19 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Price July 16, 1940 Krogh Nov. 24, 1942 Schwien Dec. 18, 1945 Noxon Mar. 5, 1946 Warner et a1 Dec. 3, 1946 Maxson Dec. 24, 1946 Jepson et a1. Jan. 14, 1947 Cooper et a1 Apr. 29, 1947 Morris July 22, 1947 Kemper Sept. 30, 1947 Number Number Name Date Dube Dec. 23, 1947 Paget May 18, 1948 Teague Aug. 24, 1948 Bechberger Sept. 28, 1948 Cooper et a1. Oct. 12, 1948 Widgery et a1 Mar. 1, 1949 Del Mar Apr. 17, 1951 Del Mar Apr. 17, 1951 Klemperer Apr. 17, 1951 FOREIGN PATENTS Country Date .France Nov. 8, 1920 Great Britain May 27, 1940 

